The invention relates to a system and method for counting objects in a scanned image, and particularly to a system and method for counting colonies of micro-organisms in a culture media.
Detection and counting of micro-organisms is a universal problem in many diverse fields. Micro-organisms occur in almost all foods, in water, in air, and on numerous surfaces and substances with which humans come in contact. Such micro-organisms are often harmful and therefore must be measured and controlled.
A widely used practice for measuring the presence of micro-organisms is to place a sample of the substance to be tested, suitably prepared, on a nutrient surface such as agar, and to allow the micro-organism to grow into colonies. Standard dishes for use with such nutrient materials are called petri dishes, and a widely used commercial replacement for petri dishes is a film product provided by 3M under the trademark Petrifilm. When cultured in such a medium, colonies become visible to the eye and can be counted. Each visible colony corresponds to one original micro-organism.
An example wherein such a test occurs is in the dairy industry, where every shipment of milk from every farm must be tested for harmful bacteria. The accuracy of the count of colonies is of critical importance. Automatic counting machines have been available in the past, but their use is limited. One reason for this is that many unique problems arise that require the judgement of a human counter. Bacteria of different types produce colonies with diverse appearance that must be counted separately. Further, colonies may be small and light, large and dense, or clumped into large masses that overlap. Colonies may also have differing color or surface qualities, may produce gas bubbles, and may liquify the nutrient material thereby spreading over wide areas. Existing colony counter devices use binary (black and white) images wherein much of the detail information about objects is lost. Such devices are largely incapable of dealing with the afore-described problems in counting colonies.
There is therefore a need for a system and method for counting colonies that is capable of separating various objects that occur in a petri plate or other media so as to provide a more accurate count of colonies.
It is therefore the primary object of the present invention to provide a method for counting objects in an image wherein accuracy of the count is enhanced.
It is a further object of the present invention to provide a system for carrying out the method of the present invention.
It is still another object of the present invention to provide a system and method as above which corrects the count of objects or colonies based on one or more colony object characteristics such as: visibility, object color, object proximity, object vicinity, object shape, and object spreading.
Other objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages are readily attained.
According to the invention, a method is provided for counting objects in an image, which method comprises the steps of: (a) providing an image including at least one object defined in said image in shades of at least one color; (b) identifying objects in said image having a shade of color which exceeds a threshold shade so as to provide a number of identified objects; (c) evaluating objects of said number of identified objects based upon object criteria to determine whether each object satisfies said criteria and can be counted, or does not satisfy said criteria and is suspect and needs further analysis; (d) repeating steps (b) and (c) for objects which are suspect at shades of color increasingly exceeding said threshold shade until all objects satisfy said criteria; and (e) providing a count of said objects, whereby accuracy of said count is enhanced.
In further accordance with the invention, objects are filtered and may be rejected or not counted based upon object visibility, color, proximity, vicinity, shape and spreading so as to adjust the count of objects for these sources of inaccuracy.